The present invention refers in general to a restraint system for car safety seats for children, the restraint system being indifferently of the type with three or five mounting points and comprising three belts, namely a lower belt and two upper belts, which can be releasably connected to each other by means of a fastening device comprising a buckle and two tongue-like coupling elements, the buckle comprising a case attached to the free end (upper end) of the lower belt and a coupling mechanism arranged to releasably (to this end, the coupling mechanism comprises a release button operable by the user) engage the two tongue-like coupling elements, each of which is connected to a respective upper belt, when both the tongue-like coupling elements are inserted into the case of the buckle. More specifically, the present invention refers to a device for indicating the correct tensioning intended for a restraint system of the above-identified type.
Once the three belts have been connected to each other by means of the fastening device, in order to ensure that the body of the child sitting in the seat is safely restrained, it is necessary to tension the belts with a given minimum tension level. In order to allow the user to realize when the correct tension level in the belts has been reached, it is known the use of indicator devices which provide a visual indication of the condition of correct tensioning of the belts. These known indicator devices typically comprise one or more springs through which the lower belt is connected to the case of the buckle, in such a manner that the spring(s) is(are) elastically deformed depending on the tension force acting on the lower belt and therefore cause a relative movement between the lower belt and the case of the buckle, and an indicator element (separate from the release button) having a visual symbol, such as for instance a red- or green-coloured rectangle, which in the condition of correct tensioning of the belts can be seen by the user through a special window provided in the case of the buckle to give a visual indication that the condition of correct tensioning has been reached, wherein the indicator element is mounted in the case of the buckle so as to move, as a result of the relative movement between the lower belt and the case of the buckle, between a first end-of-travel position, corresponding to the condition of loose belts, in which the visual symbol on the indicator element is not visible through the window provided in the case of the buckle, and a second end-of-travel position, corresponding to the condition of correct tensioning of the belts, in which the visual symbol on the indicator element is wholly visible through the window provided in the case of the buckle. The spring (or the springs) and the indicator element are designed in such a manner that the indicator element takes the aforesaid second end-of-travel position when the tension force applied on the lower belt has reached the desired value. The user which fastens the belts knows then that he shall tighten the belts on the body of the child until the visual symbol on the indicator element in the buckle is visible through the respective window. The main problem of such a known indicator device is that once the belts have been correctly tensioned, the indicator element does not permanently remain in the aforesaid second end-of-travel position in which it indicates the condition of correct tensioning, but it may move towards the first end-of-travel position due to relative movements between the lower belt and the case of the buckle. The user who, after having correctly fastened the belts, notices a change in the indication provided by the indicator device may therefore be confused by that and led to tension the belts again, even if not necessary.